Conventionally, as head chips that deform a driving wall by applying a voltage to the drive electrode formed on the drive walls that segment channels, and that use the pressure generated at that time to eject the ink in the channel from a nozzle, the so called harmonica type head chips are known in which opening parts are provided respectively on the front surface and the back surface.
In such harmonica type head chips, the problem is how to carry out electrical connection between each drive electrode and the drive circuit.
For example, conventionally, an inkjet head has been proposed (Japanese Unexamined Patent Application Publication No. 2004-90374) in which, by providing a penetrating electrode in the cover substrate of the head chip that covers the top part of the channel, the drive electrode inside each channel is brought out to the surface of the cover substrate of the head chip, and the electrical connection between the different drive electrodes and the drive circuit is attempted to be made on the surface of this cover substrate by an FPC, etc., in which the interconnections for driving have been made.
However, providing a penetrating electrode in the cover substrate requires difficult and complicated operations such as, the operation of opening a penetrating hole in the substrate material which is made of a ceramic, etc., and the operation of embedding electrically conductive material inside the penetrating hole, etc. Because of this, an inkjet head has been proposed (Japanese Unexamined Patent Application Publication No. 2006-82396) in which the electrical connections between the different drive electrodes and the drive circuits are made by drawing out and forming, on the back surface of the head chip which is the surface on the side opposite to the surface from which the ink is ejected, connection electrodes that are electrically connected to the different drive electrodes, bonding an interconnection substrate to this back surface of the head chip, and joining an FPC on the edge part of the interconnection substrate.
Forming by drawing out from each channel the interconnection electrodes that are electrically connected to the drive electrodes on the back surface of the head chip in this manner makes it possible to draw out and form the interconnection electrodes easily and also with high accuracy compared to providing penetrating electrodes in the cover substrate, because this can be carried out using the patterning method of the common metal thin films.
However, in the case of a head chip in which higher density is aimed at by providing in parallel two or more rows of channels in a multiple channel construction, since the channel rows are close to one another, it is difficult to draw out the interconnection electrodes up to the edge part of the head chip. For example, in the case of a head chip having two rows of channels, Channel A and Channel B, there is the problem that it is difficult to draw out and form the interconnection electrodes from the channels of row B to the edge part of the head chip on the side that has to go over the channels of row A. This is because it is necessary to go over the channels of row A.
Here, when all the channels of a head chip having a plurality of rows of channels are ejecting channels that eject ink, in general, the channels of the neighboring rows of channels are placed so that they are shifted from each other by half a pitch. In this case, although it is possible to consider carrying out patterning so that the connection electrodes extending from the channels of row B are passed in between the channels of row A and extend up to the edge part of the head chip on the side of that row A, there are the following problems.
When carrying out patterning so that the connection electrodes extending from the channels of row B are passed in between the channels of row A and extend up to the edge part of the head chip on the side of that row A, the connection electrodes are formed in close contact on the drive wall surfaces that face the back surface of the head chip. Because of this, when a drive voltage is applied to the connection electrode during driving, the drive wall is likely to have electrostatic capacitance due to this drive voltage applied to the connection electrode. If the drive wall has electrostatic capacitance, there is the problem that the deformation speed of the drive wall goes down, and it is not possible to obtain the prescribed ink ejecting performance.
Further, in order to pattern connection electrodes between channels, although multilayer formation is done by evaporating the metal for electrode formation after forming a mask covering so as to expose the drive wall surface facing the back surface of the head chip which is the part in which the connection electrode is formed, it is necessary to make the width of the exposed region of the drive wall surface facing the back surface of the head chip smaller than the width of the drive wall in order to acquire the mask adhering region, and also, to prevent short circuits with the drive electrode facing the inside of the channel. As a consequence, it is inevitable that the connection electrode has a shape with a considerably small width compared to the width between the channels, and there is the possibility of the electrical connection being broken.
In view of this, the purpose of the present invention is to provide an inkjet head in which it is possible to carry out easily the electrical connections with FPC, etc., by providing in parallel each of the connection electrodes drawing out from each of the ink channels on the edge part of the back surface of a honeycomb type head chip in which a plurality of rows of channels are provided with all the channels being ejecting channels.